|Publication number||US4868390 A|
|Application number||US 07/156,395|
|Publication date||Sep 19, 1989|
|Filing date||Feb 16, 1988|
|Priority date||Feb 16, 1988|
|Publication number||07156395, 156395, US 4868390 A, US 4868390A, US-A-4868390, US4868390 A, US4868390A|
|Inventors||Hans J. Keller, Fredrick Villers|
|Original Assignee||Eltec Instruments, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (1), Non-Patent Citations (2), Referenced by (25), Classifications (5), Legal Events (7)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates to an arrangement for a radiation sensor with at least one pyroelectric element. The electrical signals produced by the pyroelectric element are intensified by means of a electronic amplifier and fed to an output terminal.
It is an objective of the present invention to provide an arrangement of pyroelectric elements, resistors and amplifiers to reduce the noise sources as far as possible, and to provide a sensor element with the highest possible sensitivity to the radiation and the smallest possible noise signal.
This is accomplished by means of a current amplifier, wherein the feedback resistor has such a high resistor value that its noise can be neglected, and including a compensation amplifier that eliminates or reduces the input current noise.
FIG. 1 is a circuit diagram of a sensor in accordance with the invention;
FIG. 2 shows a series modification to the sensor of FIG. 1;
FIG. 3 shows a parallel modification to the sensor of FIG. 1; and
FIG. 4 shows an alternative embodiment of sensor using a resistor in place of diodes.
The invention is described in terms of an illustrative radiation sensor.
FIG. 1 shows such a circuit arrangement in detail. The pyroelectric element 1 is connected between the negative rail 10 and the wire connection 13. The wire 13 leads to the positive input 14 of the compensation amplifier 2 and also to the negative input 17 of the main amplifier 9. The compensation amplifier 2 as well as the main amplifier 9 are standard differential operational amplifiers. Both amplifiers are operated from the positive supply voltage 12 and the negative rail 10. In the compensation amplifier 2, the output 16 is connected with the negative input 15 to form an amplifier with unity gain. The output of the compensation amplifier 2 is connected by means of the diodes 3 and 4 with the pyroelectric element over the wire connection 13. Also, a reference voltage is provided on the point 20, for example by means of the zener diode 5 and the current source 6. This reference voltage is supplied through the resistor 7 onto the positive input 18 of the main amplifier 9. The output 19 of the main amplifier is connected with the signal output 11 of the sensor arrangement. The feedback resistor 8 is connected between the output 19 and the negative input 17 of the main amplifier 9.
The operation of this arrangement is as follows: The pyroelectric element 1 produces an electrical signal on its output wire 13 according to the incident radiation. A similar signal appears also on the output 16 of the compensation amplifier 2. It is identical with the signal on 13 except for the imperfections of the amplifier 2. Therefore, the electrical voltage over the two diodes 3 and 4 is zero or almost zero. As the diodes 3 and 4 are passive elements, the current flow through the diodes 3 and 4 is also zero or almost zero. Therefore, the diodes 3 and 4 have no effect on the operation of the circuit. The output signal of the pyroelectric element is also fed by means of the wire 13 to the main amplifier.
Except for unwanted parasitic effects, the output voltage at point 11 is identical to the current produced by the pyroelectric element multiplied with the resistor value 8. If the resistor value of the resistor 8 is increased, the output voltage on 11 can be increased to any desired magnitude. If isolated input transistors are used in the amplifiers 2 and 9, the resistor 8 can be increased up to the order of magnitude of the electrical conductivity of the materials used. In a practical application, the value of the resistor 8 can be between 10E11 or 10E13 ohms. Hoewver, such amplifiers with isolated inputs have the disadvantage of being easily destroyed by high electrical voltages. This is of specific importance because the pyroelectric element 1 can easily produce voltages on the order of 100 volts or more upon changes of the ambient temperature. In such cases, the compensation amplifier circuit becomes operational.
When the signal voltage on wire connection 13 exceeds the positive voltage on connection 12 or goes below the negative voltage of rail 10,, the output voltage at compensation amplifier output 16 cannot track the voltage on 13 anymore. If this occurs, the voltage over the diodes 3 and 4 raises above zero and either the diode 3 or the diode 4 becomes conductive. Thereby, the charge on the pyroelectric element on the wire connection 13 is discharged until the time when the voltage difference between line 13 and output 16 becomes low enough, the diodes 3 and 4 stop being conductive, and the normal operating conditions are reached again.
Instead of the pyroelectric element 1, it is also possible to use an arrangement of two or more pyroelectric elements. FIG. 2 shows such an arrangement with two elements 22 and 23 connected in series in place of the element 1 between the connections 10 and 13. These two elements 22 and 23 can be connected with the same or with opposite polarity. It is also possible to use more than two elements in series.
FIG. 3 shows a parallel arrangement of pyroelectric elements 24 and 25. This arrangement can be used instead of one single pyroelectric element in an arrangement according to FIG. 1. The parallel connection of two or more pyroelectric elements can be accomplished by using the same or opposite polarities. The latter case is called parallel opposed circuit.
It is also possible to use other elements instead of the diodes 3 and 4. Specifically, this could be zener diodes, shockley diodes or a normal resistor 26, as shown in FIG. 4. It is only important that a current can flow between line 13 and output 16 when the voltage differential between this two points is different from zero, and that no or only an unsignificant current flows when the voltage between 13 and 16 is zero or almost zero. In a practical application, the voltage differential between 13 and 16 can very often not be made zero. Therefore it is advantageous to use elements instead of the diodes 3 and 4 that still provide very low current when the voltage differential is low, such as small geometry diodes or resistors with values on the order of 10E8 and 10E12.
It is also possible to replace the elements 5 and 6 in FIG. 1 with other elements such as a resistor network or an active element such as an integrated voltage regulator. It is only of importance, that a reference voltage at point 20 provides safe operating conditions for the amplifier 9 well within its specification. However, this reference voltage is not of any importance for the proper operation of the circuit as described in this invention.
It is also possible to eliminate the resistor 7 and to replace it by a simple wire connection. Its purpose is only to provide symmetrical conditions for the inputs of the amplifier 9. Therefore it has normally the same resistor value as the resistor 8. However, as the symmetrical conditions on the inputs of the amplifier 9 may also be determined by parasitic effects, such as stray capacitance or leakage current, there is no need for the resistor 7 and it may well perform without it. Sometimes, the resistor 7 is used to improve the power supply rejection ratio. If this is not required in a specific application, the resistor 7 can also be eliminated.
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|Citing Patent||Filing date||Publication date||Applicant||Title|
|US5357111 *||Aug 17, 1993||Oct 18, 1994||Ophir Optronics Ltd.||Pyroelectric detector apparatus|
|US5372545 *||May 25, 1993||Dec 13, 1994||Kabushiki Kaisha Toshiba||Ventilator with a sensor|
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|US7097226||Aug 31, 2004||Aug 29, 2006||Donnelly Corporation||Safety system for a compartment of a vehicle|
|US7498823 *||Jun 14, 2005||Mar 3, 2009||Telecom Italia S.P.A.||Physical quantity, particularly humidity detection device, and related detecting method|
|US8258932||Nov 22, 2005||Sep 4, 2012||Donnelly Corporation||Occupant detection system for vehicle|
|US9212951 *||Jun 30, 2011||Dec 15, 2015||Panasonic Intellectual Property Management Co., Ltd.||Object detection device|
|US20030035297 *||Oct 3, 2002||Feb 20, 2003||Donnelly Corporation||Safety system for opening the trunk compartment of a vehicle|
|US20050023858 *||Aug 31, 2004||Feb 3, 2005||Donnelly Corporation, A Corporation Of The State Of Michigan||Safety system for a closed compartment of a vehicle|
|US20080028853 *||Jun 14, 2005||Feb 7, 2008||Telecom Italia S.P.A.||Physical Quantity, Particularly Humidity Detection Device, And Related Detecting Method|
|US20130082179 *||Jun 30, 2011||Apr 4, 2013||Panasonic Corporation||Object detection device|
|EP0422385A1 *||Sep 4, 1990||Apr 17, 1991||Steinheil Optronik Gmbh||Opto-electronic circuit arrangement|
|EP0507542A2 *||Mar 31, 1992||Oct 7, 1992||Texas Instruments Incorporated||Uncooled infrared detector readout monolithic integrated circuit with individual pixel signal processing|
|WO2009036065A1 *||Sep 10, 2008||Mar 19, 2009||Suren Systems, Ltd.||Improved pir motion sensor|
|U.S. Classification||250/338.3, 250/349|
|Jun 3, 1988||AS||Assignment|
Owner name: ELTEC INSTRUMENTS, INC., 350 FENTRESS BLVD., DAYTO
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:KELLER, HANS J.;REEL/FRAME:004923/0816
Effective date: 19880510
Owner name: ELTEC INSTRUMENTS, INC., 350 FENTRESS BLVD., DAYTO
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:VILLERS, FREDRICK;REEL/FRAME:004923/0819
Effective date: 19880519
Owner name: ELTEC INSTRUMENTS, INC., A COORP. OF FLORIDA,FLORI
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:KELLER, HANS J.;REEL/FRAME:004923/0816
Effective date: 19880510
Owner name: ELTEC INSTRUMENTS, INC., A CORP. OF FL,FLORIDA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:VILLERS, FREDRICK;REEL/FRAME:004923/0819
Effective date: 19880519
|Nov 2, 1992||FPAY||Fee payment|
Year of fee payment: 4
|Sep 19, 1993||LAPS||Lapse for failure to pay maintenance fees|
|Dec 7, 1993||FP||Expired due to failure to pay maintenance fee|
Effective date: 19930919
|Dec 9, 1996||FPAY||Fee payment|
Year of fee payment: 8
|Aug 10, 2001||SULP||Surcharge for late payment|
Year of fee payment: 11
|Aug 10, 2001||FPAY||Fee payment|
Year of fee payment: 12